This invention relates to engine oil systems and, more particularly, to a system including pressure valves to optimize oil flow and pressure for various lubrication and actuation functions.
Internal combustion engines may use lubricating oil for many purposes including, for example, lubricating moving parts, actuating cam phasers, and controlling valve lifters for valve stepping and cylinder deactivation. Cam phasers and cylinder deactivation devices generally require a higher oil pressure for actuation during engine operation than the moving parts of the engine require for proper lubrication.
One approach to maximize engine efficiency is to use a smaller oil pump to provide only the minimum amount of oil pressure needed to prevent engine wear. However, smaller oil pumps do not provide enough oil pressure to actuate a cam phaser or switching lifters at low and idle engine speeds. Thus, cam phasing, valve stepping, and cylinder deactivation can only be achieved at higher engine speeds.
Another approach is to use a larger oil pump to provide enough oil pressure to operate the cam phaser or switching lifters at low engine speeds. This approach allows phasing, valve stepping, and cylinder deactivation at lower engine speeds to alter the valve timing and increase engine efficiency. However, the efficiency gains are not without cost. A higher pressure produced by larger oil pump supplies excess flow that over lubricates the moving parts of the engine and requires additional energy to drive the pump, creating parasitic losses that reduce engine efficiency.
A method is desired of selectively regulating oil pressure throughout an engine to increase engine efficiency while allowing the engine to operate a cam phaser or switching lifters at low engine speeds without having to greatly increase oil pump output.
Co-pending applications pertaining to related subject matter were filed concurrently with this application on Sep. 18, 2003 as U.S. application Ser. No. 10/666,745, U.S. application Ser. No. 10/666,864, and U.S. application Ser. No. 10/667,233.
The present invention provides an oil system for an internal combustion engine having oil pressure control valves to optimize oil pressures in the engine while increasing engine efficiency by minimizing parasitic losses created from over lubrication.
In an exemplary embodiment, the oil system includes an oil pump having an inlet and an outlet. An oil pickup connected with the inlet extends into an engine oil sump to draw oil into the oil system. The outlet of the oil pump connects to a main oil feed which supplies oil to a main bearing gallery and a cam phaser. Oil sent to the cam phaser is used to actuate the cam phaser, while oil directed to the main bearing gallery is used primarily for lubrication purposes. In addition, some of the oil pumped into the main bearing gallery is sent through a cam gallery feed to a cam gallery in an upper part of the engine for lubrication of a valve train. When switching lifters are present, some of the oil directed to the cam phaser or the cam gallery may be diverted to the switching lifters to allow valve stepping or cylinder deactivation.
A first pressure increasing valve connected between the main oil feed and the main bearing gallery has a small opening designed to provide minimal oil flow to the main bearing gallery while oil pump output is low. As oil pump output increases, the pressure increasing valve reacts by providing additional openings to allow for addition flow through the valve.
The restriction of oil flow created by the first pressure increasing valve increases oil pressure to the main oil feed and the cam phaser while the main bearing gallery operates at a lower oil pressure. This allows cam phasing at engine idle or other conditions when oil pump pressure is normally to low to actuate the cam phaser. The additional oil pressure supplied to the cam phaser allows the phaser to vary valve timing at all engine speeds without a large increase in the size of the oil pump. The use of a smaller oil pump reduces parasitic losses for increased engine efficiency.
A second pressure increasing valve connected between the main bearing gallery and the cam gallery has a small opening designed to provide minimal oil flow to the cam gallery while oil pump output is low. As oil pump output increases, the pressure increasing valve reacts by providing additional openings to allow for additional flow through the valve.
The restriction of oil flow created by the second pressure increasing valve increases oil pressure to the main bearing gallery, while the cam gallery operates at a lower oil pressure. This allows the cam gallery to operate at a lower oil pressure than the main bearing gallery to reduce engine oil demands, thereby allowing the engine to operate with a smaller oil pump to reduce parasitic losses and increase engine efficiency.
A pressure regulator valve positioned between the second pressure increasing valve and the cam gallery regulates pressure to the cam gallery to control the switching lifters for valve stepping or cylinder deactivation. When low valve step operation is desired, the pressure regulator valve maintains low oil pressure to the switching lifters. When high valve step operation is desired the pressure regulator valve maintains high oil pressure to the switching lifters to cause high valve lift. When the switching lifters are used for cylinder deactivation, the pressure regulator valve may be used to provide adequate oil pressure for cylinder deactivation or normal oil pressure for standard engine operation.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.